The halo by halo missing baryon problem

Abstract

The global missing baryon problem - that the sum of observed baryons falls short of the number expected form BBN - is well known. In addition to this, there is also a local missing baryon problem that applies to individual dark matter halos. This halo by halo missing baryon problem is such that the observed mass fraction of baryons in individual galaxies falls short of the cosmic baryon fraction. This deficit is a strong function of circular velocity. I give an empirical estimate of this function, and note the presence of a critical scale of ~900 km/s therein. I also briefly review Omega_b from BBN, highlighting the persistent tension between lithium and the CMB, and discuss some pros and cons of individual galaxies and clusters of galaxies as potential reservoirs of dark baryons.

10 pages, review for IAU Symposium 244, Dark Galaxies & Lost Baryons

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Cited by in corpus (5)

• Ultra-Light Dark Matter
• Detection of the kinematic Sunyaev-Zel'dovich effect with DES Year 1 and SPT
• MUSE-ALMA Haloes VII: Survey Science Goals & Design, Data Processing and Final Catalogues
• The hot gas distribution, X-ray luminosity and baryon budget in the L-Galaxies semi-analytic model of galaxy formation
• The Galactic Pizza: Flat Rotation Curves in the Context of Cosmological Time-Energy Coupling